I was recently discussing a published case study on my last bodybuilding contest prep  with some of my professors. During this discussion, the topic of refeed days came up. I mentioned the proposed benefits of refeed days: keeping metabolic rate elevated, improving workout performance, increasing muscle retention while dieting, and providing a mental break to help prevent binging, and was asked if I had any scientific evidence to back up these claims. I didn’t have a great answer. From an applied standpoint, I knew a majority of successful bodybuilders do not eat the same macronutrient distribution daily while dieting for a contest and most incorporate things like: carb cycling, refeed days, cheat meals, cheat days, etc. This approach is even something most individuals who use a science-based approach and broscientists would agree on. Therefore, I assumed there had to be something to it or it wouldn’t be so widely incorporated into bodybuilding contest prep plans. However, I was not sure if this was another example of an approach that bodybuilders use that science hasn’t caught up to or if there was science to support this practice so I decided to dig into the scientific literature and see what I could find. What follows is a summary of peer-reviewed scientific literature related to refeeding.
Metabolic Rate/Fat Loss:
Many individuals incorporate refeed days while dieting in an attempt to keep metabolic rate elevated. This rationale for this is centered on leptin, a hormone secreted from fat cells . Reductions in fat cell size or energy intake (both of which happen while dieting) decrease leptin secretion . In obese individuals, reductions in plasma leptin concentrations of 36% in 4 days  and 54% in 1 week  of energy restriction have been observed. Leptin levels in bodybuilders during contest prep are lower than those observed in obese participants. A recent case study following a professional natural bodybuilder during a 6 month contest preparation observed leptin levels below the normal range (3.7 – 11.1 ng/ml) at the start of contest preparation which were further decreased to 1.36 ng/ml by the end of contest preparation .
Similarly, thyroid hormone concentrations are reduced during periods of energy restriction such as fasting  or bodybuilding contest preparation . Both thyroid hormone and leptin are involved in regulation of metabolic rate and reductions in these hormones during dieting contributes to metabolic adaptation observed . In fact, a reduction in metabolic rate of 30-40 percent has been observed during natural bodybuilding contest preparation . This is comparable to the 40 percent reduction in total daily expenditure observed in the Minnesota semi-starvation study. Twenty-five percent of this reduction could be explained by the loss of body weight; however, the other 15 percent reduction was the adaptive component resulting, in part, from reduction in leptin and thyroid hormones .
Amenorrhea (loss of menstrual cycle) is common in female competitors during contest preparation as a result of energy restriction and low body fat . Loss of menses is associated with suppression of estrogen and a reduction in metabolic rate . Studies examining the effect of refeeding following fasting have shown that luteinizing hormone (the hormone that drives estrogen production) pulsation may become more normal following refeeding . Therefore, refeeding may help preserve estrogen levels and preserve metabolic rate in dieting females.
Reductions in multiple hormone systems contribute to metabolic adaptation observed while dieting, but how do refeed days affect this? In theory, a refeed day is a higher energy day which elevates leptin, thyroid hormone, and potentially estrogen, thereby increasing metabolic rate and weight loss. However, as a whole, long-term studies (primarily in obese participants) do not support this claim likely because these hormones fall quickly once energy intake is restricted the day following a refeed. Varaday et al.  performed a review comparing weight loss studies in obese individuals using either a continuous daily caloric restriction or interventions where caloric intake was not constant daily. No differences in weight or fat loss were observed between diet types. Harvie et al.  compared the effects of the pattern of caloric reduction in obese women during a 6 month weight loss intervention. All participants consumed a weekly energy deficit of 25 percent. One group had a continuous daily energy deficit while the other group had a larger deficit for 2 days and ate at maintenance for the other 5 days. No differences body weight or body fat losses were observed. Similar results have been observed in other human  and animal  studies. These results suggest that weekly caloric deficit is more important for fat loss than the pattern of caloric deficit. However, it is important to highlight that these studies where done in obese participants who primarily were not participating in exercise programs. The effects of refeeding on metabolic rate and fat loss in dieting lean individuals who are training hard have not been directly studied.
Refeeds are often performed on the day of or day prior to the most difficult workout of the week to improve exercise performance. This is likely related to muscle glycogen, a storage form of carbohydrates used for energy during exercise. During dieting, muscle glycogen stores are reduced . Weightlifting  and cardio  both further reduce glycogen concentration and training in a glycogen-depleted state has been shown to reduce weightlifting performance . A refeed day replenishing muscle glycogen stores prior to a tough workout should increase performance during the workout, but this has not been studied in lean athletes. However, from personal experience, performing a refeed day on the day prior to a tough workout tends to improve energy, strength, and overall workout quality; therefore, I would hypothesize that future studies done on this topic would support this claim.
Refeeding has been proposed to help maintain muscle mass while dieting through improvements in workout performance (as discussed above), potentially increasing testosterone concentrations, and increasing insulin concentrations. Testosterone is an anabolic hormone that is reduced during an energy deficit; however, when energy balance is restored testosterone levels increase, likely through an increase in leptin . In fact, exogenous (injected) leptin has been shown to normalize the reduction testosterone concentration in an animal model of fasting . Theoretically, this should mean increased in muscle mass retention with refeeding during dieting.
Insulin is another anabolic hormone that is reduced during natural bodybuilding contest preparation . In a study of male bodybuilders preparing for competition, reductions in insulin were significantly correlated with loss of lean mass while testosterone was not suggesting that reductions in insulin may be driving muscle loss during contest preparation . Therefore, a refeed high in carbohydrate may increase insulin concentrations and reduce muscle loss in dieting bodybuilders.
Although there are a number of potential mechanisms by which refeeding may preserve muscle mass while dieting, the effects of refeeding on muscle retention while dieting have not been well studied in lean individuals. However, some research has been done on the pattern of energy deficit during weight loss in obese participants. A review comparing weight loss studies using continuous caloric restriction to other studies using intermittent caloric restriction observed greater muscle maintenance with intermittent restriction . However, studies directly comparing continuous and intermittent caloric restriction patterns have observed no difference in muscle retention .
In recent case studies of dieting bodybuilders, competitors that incorporated refeed days  observed a lower percentage of weight loss as lean mass those who did not  suggesting that refeed days may increase muscle retention while dieting. However, these results should be interpreted with caution because the bodybuilders consumed different macronutrient ratios and performed different weightlifting and cardio regimens. Future research is needed to determine the effects of refeed days on muscle maintenance during contest preparation; however, it is possible that this claim may be supported in the future.
Refeed days may help reduce hunger and the likelihood of binging through increasing leptin. Leptin is correlated with feelings of fullness and reduced hunger . In addition, low leptin concentrations are associated with increased food reward, increasing risk of binging . However, as mentioned previously, leptin levels increase in response to refeeding, but quickly decrease once an energy deficit begins the following day. Therefore, it is not clear if increasing leptin through a refeed day effects hunger and binging.
Another benefit of a refeed day is that it allows an individual to fit in other foods they may be craving more easily. By having this diet flexibility, risk of binging may be reduced . From an applied standpoint, this mental break is one of the most beneficial effects of a refeed day for many individuals and may make performing refeeds beneficial, regardless of if other claims prove to be untrue.
- Carbohydrates have a larger effect on leptin and thyroid levels than fat or protein ; therefore, a high-carbohydrate is likely more beneficial than a high-fat or high-protein refeed.
- Research on the size of refeeds has not been performed; however, larger fluctuations in energy fluctuation may not be optimal for workout performance and lean mass retention when individuals are very lean.
- Refeed frequency has also not been studied; however, it is possible that more frequent refeeding may be necessary during the later stages of dieting when bodybuilders are leaner and leptin levels are lower.
- From an applied standpoint, performing refeed days with macronutrient targets may be more beneficial than cheat days because it will allow for more precise control of total weekly caloric intake.
Practical Application: What should I do on my refeed days?
Refeed days are performed by increasing carbohydrate intake. The extent to which carbohydrates are increased largely depends upon the individual. Some individuals have highly adaptive metabolisms and respond better to larger increases in carbohydrate while others tend to gain a decent amount of weight following a refeed and respond better to smaller refeeds. Protein and fat are generally kept constant on a refeed day during the earlier stages of a diet, but may be reduced slightly from non-refeed days deeper into a diet to help maintain a weekly caloric deficit.
For someone in the early phases of a diet, refeed frequency may only need to be every 7-10 days; however, later in the diet it may be beneficial to increase refeed frequency to around twice weekly. However, the size of a refeed generally needs to be reduced as the frequency of refeed days is increased to maintain a weekly caloric deficit.
There is not a one size fits all approach to refeeding. I encourage individuals to experiment with refeed size and frequency to determine what works best for them. A good way to gauge if a refeeding strategy is right for you is to observe how long it takes for bodyweight to come back down following a refeed day. If it is taking bodyweight until the next refeed day to drift down to pre-refeed weight, the size and/or frequency of your refeeds is likely too high.
Further research is needed to determine if refeeding while dieting is beneficial in lean athletes. It is possible that a bodybuilder could get the same results without refeeding as long as weekly caloric deficit is the same; however, much more work is needed before this question can be definitively answered. In the meantime, I will continue to incorporate refeed days while dieting because I enjoy the mental break it gives me and hope that additional scientific research will be done on this topic.
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